Flying, trample
Whenever an opponent casts a spell, that player creates a Blood token. (It's an artifact with "{1}, {T}, Discard a card, Sacrifice this token: Draw a card.")
Whenever this creature attacks, it gets +1/+0 until end of turn for each Blood token defending player controls.
If an effect refers to a Blood token, it means any artifact token with the subtype Blood, even if it has gained other subtypes.
Some triggered abilities trigger "whenever you sacrifice a Blood token." These abilities trigger regardless of why you sacrificed that Blood token.
You can't sacrifice a Blood token to pay multiple costs.
Only Blood tokens controlled by the player Bloodvial Purveyor is attacking or the controller of the planeswalker it's attacking are counted to determine the bonus from its last ability.